The parent case Ser. No. 005,138 related to the preparation of 3-menthene and more particularly to a novel selective hydrogenation process utilizing a homogeneous ruthenium catalyst complex therefor.
It has now been found that d-3-menthene of high optical purity can be produced by the selective hydrogenation of d-isolimonene in the presence of minor amounts of a palladium hydrogenation catalyst at temperatures up to about 200.degree. C. and pressures of preferably about 100-500 psig. Such selective hydrogenation process for the production of d-3-menthene of high optical purity is surprising in view of U.S. Pat. No. 3,407,241 (Booth) which teaches the selective conversion of d-trans-isolimonene predominantly to d-trans-2-menthene in 78 percent conversion with the production of no 8-menthene.